The release into the environment occurs either directly, e.g. via sunscreen use at the beach, or indirectly after wastewater or waste treatment (see cross-cutting topics - nanomaterials in waste & nanomaterials in waste water treatment). The material flow analysis quantifies all material flows for the nanomaterials and the corresponding nanoproducts. This allows simplified calculations of the environmental concentrations in a specific area (e.g. soil). These nanomaterial flows into the environment constitute also a basic input for environmental fate models.


The Environmental Fate Modelling

With environmental fate modelling the transport, transformation and degradation of nanomaterials in the environment can be predicted. These calculations not only consider the properties of the nanomaterials but also the interactions with water and soils, e.g. Solubility or Agglomeration. With the help of these fate models it can then be predicted if a nanomaterial is transported over long distances or if it is deposited rapidly, e.g. in sediments.


Modelled Concentrations

The most important information for the calculation of the environmental concentrations is the production quantity of a nanomaterial, the life cycle of the most important nanoproducts, the amount of nanomaterials removed via waste water treatment and waste disposal, and the fraction recovered during recycling.

Generally, nanomaterials produced in larger quantities have higher environmental concentrations than those who have only limited applications. However, the life-cycle of the nanoproducts has a large influence on the actual release. A large release occurs for example from cosmetics. Because of the efficient removal of nanomaterials during wastewater treatment, large amounts are transferred into sewage sludge. When sludge is used as fertiliser on agricultural fields, high concentrations of nanomaterials in these soils can be expected.

Predicted environmental concentrations of nanomaterials in surface waters and sludge-treated soils. Mostly, higher concentrations of nanomaterials are predicted in sludge-treated soils. This is due to the removal of nanomaterials in sewage treatment plant and the subsequent deposition in the sewage sludge.

Image: Andreas Mattern/ UFZ Leipzig

Generally, the calculations show that a large part of the nanomaterials either ends up in waste and is subsequently incinerated or landfilled or is contained in products that enter material recovery or recycling.

The figure shows the predicted environmental concentrations (PEC) for some nanomaterials in surface waters and sewage-sludge treated soils. Most of the nanoparticles occur in water only in a concentration of less than one millionth gram per liter, some like nanosilver even only at a level of a billionth gram per liter.

Similar calculations have been performed for other environmental compartments such as sediments and soils, but also concentrations in landfills and sewage sludge have been calculated. In sewage-sludge treated soils the concentrations of some nanomaterials like titanium dioxide are quite high and can reach even several milligrams per kilogram soil[2-7].

In general the amounts of nanomaterials in the environment can be predicted quite well using the method of exposure modelling. The modelled concentrations replace the measured environmental concentrations which cannot be obtained at the moment due to missing analytical methods. Modelled environmental concentrations are important in order to be able to make conclusions about possible effects in the environment and thus constitute one basis for environmental risk assessments.


Literature

1) NanoImpact, "Evaluation of environmental exposure models for engineered nanomaterials in a regulatory context"

2) ACS Environmental Science & Technology, "Dynamic Probabilistic Modeling of Environmental Emissions of Engineered Nanomaterials"

3) Science of The Total Environment, "Probabilistic modeling of the flows and environmental risks of nano-silica"

4) Nanotoxicology, "Are engineered nano iron oxide particles safe? an environmental risk assessment by probabilistic exposure, effects and risk modeling"

5) Journal of Nanobiotechnology, "Probabilistic modelling of prospective environmental concentrations of gold nanoparticles from medical applications as a basis for risk assessment"

6) Environmental Pollution, "Comprehensive probabilistic modelling of environmental emissions of engineered nanomaterials"

7) Environmental Science: Nano, "Redefining environmental nanomaterial flows: consequences of the regulatory nanomaterial definition on the results of environmental exposure models"

DaNa2.0 (Data and knowledge on Nanomaterials). Posted: Apr 23, 2019.

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